How to detect whether user is inside the pager/completions?

[IlanCosman]

Prompted by IlanCosman/tide#472

commandline --paging-mode only tells us if the pager is open, not if it's in use (and therefore whether pressing enter will actually execute something or if it will just bring you back to the commandline with the selection).

For example, if you type in ls to the commandline, and then hit tab, the pager will be opened to provide completions. From there you can press enter and ls will execute, or you can use the pager to select something else, for example lsblk, and pressing enter will set the commandline to lsblk, waiting for you to press enter again to execute.

Is there any way of differentiating these two cases?